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Abstract:

Phosphonates, comprise a group of organic phosphorus molecules, characterised by a direct
C-P bond, rather then the more usual C-O-P bond. Although phosphonates are resistant to
both chemical and thermal hydrolysis, there are several bacterial enzymes capable of
breaking the C-P bond, and thus liberating inorganic phosphorus.
Despite indications that phosphonates comprise 30% of the dissolved organic
phosphorus pool in the ocean, little is known of their fate, and research has concentrated on
their degradation in oligotrophic environments.
However, the quantification and speciation of phosphonate molecules in oceanic
environments remained elusive, and although some advances in analytical methodology were
made during this thesis, no significant progress was made on the central problem of the
extraction of a highly polar analyte with an affinity for divalent cations, from a highly polar,
ionic medium.
During this thesis, the widespread presence of phosphate-limitation independent
phosphonate hydrolase in genomes of marine bacteria, as well as in metagenomic libraries is
illustrated, and the presence and expression of some of these genes is illustrated in such
diverse marine environments, as coastal ocean, upwellings, coral-associated bacteria and
shellfish pathogens.
The expression of alkaline phosphatase (AP) was observed in high nutrient upwelling
environments and this was linked with the expression of phosphoacetaldehyde
dehydrogenase, a phosphonate-degrading enzyme also thought to be under pho regulon
control. A possible mechanism involving carbon source activation of the pho regulon under
euthrophic conditions is illustrated in the shellfish pathogen, Vibrio Tubiashii, which questions
the assumption that DOP utilisation is only important during oligotrophic conditions.